Variable resistance device



June 30, 1953 w, JACK ETAL VARIABLE RESISTANCE DEVICE Filed Jan. 2, 1952INVENTOR3 WILLIAM R. JACK 8 BY LYSLE D. (PAH/LL vATTORNEY DEGREESPatented June 30, 1953 VARIABLE RESISTANCE DEVICE William R. Jack andLysle D. Cahill, Chagrin Falls, Ohio; said Cahill assignor to said JackApplication January 2, 1952, Serial No. 264,454

7 Claims. (Cl. 201-55) This invention relates to variable resistancedevices and has for one of its primary objects to provide a variableresistance device capable of permanent operation and having a wide rangeof resistance.

In the conventional variable resistance devices resistance elements ofvarious materials are employed as single or multiple coatings on aceramic base. Due to the selection of resistance materials and themethods employed in applying them to the base, inherent weaknesses inthe resistance materials develop due to heat, oxidation and otheratmospheric eilects and by reason of excessive wear by engagement withthe contactor, leaving it difiicult, if not impossible to obtainuniformity of the variable resistance device or its accurate control.This is especially true in such devices employing bases wrapped withwire, whether the bases contain any other material in addition to thewire.

It is therefore an object of this invention to provide a variableresistance device in which the resistance structure is so applied to theinsulating base as to be virtually an integral part of the base,constitute a permanent resistor impervious to oxidation and otheratmospheric effects and present an, efiicient wear resisting contactingsurface for the movable contactor.

Another object is to provide a variable resistance device in which thesurface of the base is purposely predeterminally roughened and theresistance metal structure is so predeterminedly applied thereto as tobe of progressively varying width or thickness, or both, so that thewear on the resistance metal resulting from the engagement therewith bythe movable contact, will be at a constant percentage throughout itslength, rather than at a constant amount, so as to insure longer wearand greater accuracy in performance.

With the foregoing and other objects in view, the invention resides inthe combination of parts and in the details of construction hereinafterset forth in the following specification and appended claims, certainembodiments thereof being illustrated in the accompanying drawings, inwhich:

Figure 1 is an end view of the variable resistance device, with thecover plate shown partly broken away;

Figure 2 is a view in longitudinal section of the same;

Figure 3 is a view in perspective of the ring,

partly broken away, showing a potentiometer formed of a base providedwith a resistance material structure of varying thickness and width;Figure 4 is a view in cross section taken through the base and thewidest and thickest portion of the resistance metal, the maximum wearline being indicated in dotted lines;

Figure 5 is a similar view showing the metal to have been worn off downto the wear line of Figure 4;

Figure 6 is a view in cross section taken through the base and thethinnest and narrowest portion or" the resistance metal, the maximumwear line being shown in dotted lines;

Figure '7 is a similar view showing the metal to have been worn oil downto the wear line of Figure 6; and

Figure 8 is a graph laid out in resistance versus degrees showing ourdevices performance on original calibration and calibration after wearas compared to standard wire wound potentiometers.

Referring more particularly to the drawings, the variable resistancedevice may comprise a cylindrical casing I having a cover plate 2removably secured to the casing by screw bolts 3. Suitably positionwithin the casing l is a cylindrical potentiometer ring comprising abase 4 and a resistance material structure, generally indicated at 5, onthe inside surface of the base. The casing also has an externally screwthreaded sleeve 6 for the proper mounting of the unit wherever desiredand shaft "i is mounted to be rotatable therein. Shaft l carries aflange 8 that carries a resilient arm 9 provided with a ball H urgedagainst contact element H of terminal [2. Terminal l3 has a resilientmember I4 in contact with the potentiometer ring. Flange 8 also carriesa roller contactor 55 mounted on a pin I6 and resiliently urged intoconstant contact with the inner surface of the resistance materialstructure on the inside of the potentiometer ring by a spring ll.

While the be se i may be ceramic, glass, or other suitable material, forpurposes of illustration it vill be referred to as a glass cylinder. Aspreviously stated, we desire to obtain a potentiometer ring having aresistance material structure that is virtually an integral part of theglass ring 4. This we propose to accomplish, for instance, byevaporating a resistance metal on to the inner surface or" the glassring. For purposes of illustration, Nichrome will be discussed as apreferable example. In order to evaporate the Nichrome on to and intothe glass ring, we heat the Nlchrome to a temperature above its boilingpoint in a vacuum and apply a potential between the evaporating metaland the glass ring. An alternate method is known as sputtering in whichthe cathode material is not heated, but a high potential between theanode and the cathode is used. We have found that such an evaporatedmetal process is readily controllable to insure imbedding of theNichrome into the glass ring and provide a coating whose thickness andwidth is also readily controllable for any desired resistance metalpattern of varying thickness or width or both. A single layer resistancemetal structure is shown in Figure 3 at as progressively increasing inWidth and thickness from a thin norrow end l8 to a thick wide end l9. InPatent No. 2,537,671 we mention the possibility of employing a contactorarm carrying a ball of mercury as the element that actually engages theresistance meta1 structure because of its frictionless non-wearingcharacteristics in order to protect the thin' coating of resistancemetal against wear and de terioration.

In our present invention we may employ a roll-- er such as shown at l5as the movable contactor. However, we have found that when a roller isused as the contacting element of the movable contactor, either in theconventional wire wound type of potentiometer, or even the type ofresistance metal structure, and the method of applying it to the glassring, disclosed in our above mentioned patent, the wear on theresistance metal structure is constant in amount throughout the lengthof the resistance metal structure pattern and hence calibrations inpotentiometers of non-linear characteristics after a short usage of thedevice shows it to be entirely unreliable for its intended purposes.Hence, we have evolved an improved method of applying the resistancemetal by evaporation thereof under vacuum conditions on the glass ringso that the resulting wear on the resistance metal by the roller will beconstant in percentage throughout the length of the resistance metalpattern, rather than constant in amount. In order to accomplish this wepurposely roughen the inside surface of the glass ring, by lapping oretching or the like, such roughened surface being indicated at 2!) inFigures 4 to '7, inclusive. Moreover, this roughening operation on thesurface is under fine degree control. By controlled evaporation of theresistance metal on the roughened. surface we are able to control suchmetal deposit to form any desired pattern, such as one thatprogressively increases from a thin-narrow end IE to a relatively thickwide end l9. As shown in Figure i, the resultant deposit, shown at 19,shows the resistance metal at the thick wide end to initially fill thehollows of the roughened surface 2:] and to protrude thereaboveequidistantly in the amount that it fills the hollows 20 of theroughened glass ring 4. As stated before, the pattern of resistancemetal deposit on the roughened surface 20 of the glass ring 4 mayprogressively decrease in width and thickness towards the opposite endHi, this opposite end It! being shown in Figure 6 by comparison with theother thick wide end IQ of Figure 4. In both Figures 4 and 6 we haveindicated in dotted lines 2| the wear line of the roller to be such thatoccurs when the roller eventually wears through the resistance metal tobe in contact with the glass ring, as shown in Figure '7. It will beseen, however, that when this occurs at the thin narrow end It in Figure7 there is a considerable thickness of resistance metal at the thickwide end l9 above the roughened surface 20 of the glass ring, as shownin Figure 5. Thus we obtain a constant percentage, as distinguished froma constant amount, of wear and thus increase the life of thepotentiometer as well as the reliability of the performance of thedevice. As an example, we may elect to use Nichrome as the resistancemetal and employ a roller [5 or the like, made of copper coated withsilver.

In Figure 8 we have shown a graph for comparison with curves plottedresistance versus degrees where resistance is a log function. Line Arepresents our improved device after original calibration, and dottedline B represents calibration of our device after wear, the degrees ofwear and resistance being shown to be substantially parallel in ourdevice after wear of the resistance metal from that shown in Figures 4and 6 to that shown in Figures 5 and '7. By comparison we have shown thedotted line C which represents the wear pattern of standard wire woundpotentiometers after a like amount of wear. Such a calibration showssuch a conventional device where the wear is constant in amountthroughout the length of the resistance metal pattern rather thanconstant in percentage as we obtain in our device.

We claim:

1. A variable resistance device including an insulating base having aroughened surface provided with a resistance metal structure consistingsolely of resistance metal structure deposited on said roughenedsurface, said resistance metal structure being deposited on saidroughened surface by controlled evaporation to predeterminedly obtain aconstant percentage physical resistance to wear throughout its length bymoving engagement therewith of said contacting member, and a movablecontacting member to engage said resistance metal structure.

2. A variable resistance device including an insulating base having aroughened surface provided with a resistance metal structure consistingsolely Of Nichrome as a resistance metal structure deposited on saidroughened surface, said resistance metal structure being deposited onsaid roughened surface by controlled evaporation to predeterminedlyobtain a constant percentage physical resistance to wear throughout itslength by movin engagement therewith of said contacting member, and amovable contacting member to engage said resistance metal structure.

3. A variable resistance device including an insulating base having aroughened surface provided with a resistance metal structure consistingsolely of resistance metal deposited on said roughened surface, saidresistance metal structure being deposited on said roughened surface bycontrolled evaporation to predeterminedly obtain a constant percentagephysical resistance to wear throughout its length by moving engagementtherewith of said contacting member, and a movable contacting member toengage said resistance metal, said resistance metal structure varying inthickness throughout its length.

4. A variable resistance device including an insulating base having aroughened surface provided with a resistance metal structure consistingsolely of resistance metal deposited on said roughened surface, saidresistance metal structure being deposited on said roughened surface bycontrolled evaporation to predeterminedly obtain a constant percentagephysical resistance to wear throughout its length by moving engagementtherewith of said contacting member, and a movable contacting member toengage said resistance metal, said resistance metal structure varying inwidth throughout its length.

5. A variable resistance device including an insulating base having aroughened surface provided with a resistance metal structure consistingsolely of resistance metal deposited on said roughened surface and amp-vable contacting member to engage said resistance metal, saidresistance metal structure varying in thickness and width throughout itslength.

6. A variable resistance device including a base having a roughenedsurface provided with a resistance metal structure consisting solely ofresistance metal deposited on said roughened surface, said resistancemetal structure being deposited on said roughened surface by controlledevaporation to predeterminedly obtain a constant percentage physicalresistance to wear throughout its length by moving engagement therewithof said contacting member, and a movable contacting member comprising arolling wheel to engage said resistance metal structure.

'7. A variable resistance device including an insulating base having aroughened surface provided with a resistance metal structure consistingsolely of Nichrome as a resistance metal deposited on said roughenedsurface, said resistance metal structure being deposited on saidroughened surface by controlled evaporation to predeterminedly obtain aconstant percentage physical resistance to wear throughout its length bymoving engagement therewith of said contacting member, and a movablecontact device including a rolling wheel to engage said metal. saidresistance metal structure varying in thickness and width throughout itslength.

WILLIAM R. JACK. LYSLE D. CAHILL.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,537,671 Jack et al. Jan. 9, 1951 FOREIGN PATENTS NumberCountry Date 342,300 Great Britain Jan. 28, 1931 OTHER REFERENCESCurtis, Review of Scientific Instruments, December 1933, vol 4, pages679-680.

